Field of the Application
This disclosure is directed to wireless communications and, more particularly, to call establishment for voice-over LTE (VoLTE) in networks supporting TD and FDD LTE.
Background of the Disclosure
Wireless communication systems are widely deployed to provide various communication services, such as: voice, video, packet data, circuit-switched info, broadcast, messaging services, and so on. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources (e.g., bandwidth, transmit power, etc.). These systems can be multiple-access systems that are capable of supporting communication for multiple terminals by sharing available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems and Orthogonal Frequency Division Multiple Access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless devices or terminals. In such a system, each terminal can communicate with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link can be established via a single-in-single-out (SISO), single-in-multiple-out (SIMO), multiple-in-signal-out (MISO), or a multiple-in-multiple-out (MIMO) system.
For instance, a MIMO system can employ multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas can be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≤min {NT, NR}. Each of the NS independent channels can correspond to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system can support a time division duplex (TDD) and frequency division duplex (FDD) systems. In an FDD system, the transmitting and receiving channels are separated with a guard band (some amount of spectrum that acts as a buffer or insulator), which allows two-way data transmission by, in effect, opening two distinct radio links. In a TDD system, only one channel is used for transmitting and receiving, separating them by different time slots. No guard band is used. This can increase spectral efficiency by eliminating the buffer band and can also increase flexibility in asynchronous applications. For example, if less traffic travels in the uplink, the time slice for that direction can be reduced, and reallocated to downlink traffic.
Modern wireless communication systems use 3GPP Long-Term Evolution (LTE), which is optimized for data transfer and designed as a packet switched system only. LTE does not include any circuit switched domains, which are currently used for regular wireless voice services and wireless short messaging service (SMS) services. To implement voice capability in an LTE communication system, voice-over LTE (VoLTE) will be used and various network elements and protocols will need to be upgraded to effective support VoLTE.
Therefore what is needed are effective and efficient systems and software for implanting an operable VoLTE network.